| Quote #1
Signs are small measurable things, but interpretations are illimitable, and in girls of sweet, ardent nature, every sign is apt to conjure up wonder, hope, belief, vast as a sky, and coloured by a diffused thimbleful of matter in the shape of knowledge. (1.3.6)
Dorothea is the "girl of sweet, ardent nature" being referred to in this passage. She's ready to "interpret" every "sign" given to her by Mr. Casaubon before their marriage in the best possible way, according to her own "wonder, hope, [and] belief."
| Quote #2
"I should see how it was possible to lead a grand life here – now – in England." (1.3.14)
Dorothea's dreams, hopes, and plans have to do with leading a "grand life," but she's not sure how to reconcile that ambition with the realities of everyday life. She's read a lot of histories of people who led "grand li[ves]," like Saint Theresa, but she's not sure how it can be managed in the here and now.
| Quote #3
"There would be nothing trivial about our lives. […] It would be like marrying Pascal. I should learn to see the truth by the same light as great men have seen it by." (1.3.14)
Dorothea hates "trivial" things like worrying about clothes, social visits, and what to have for dinner. She wants to spend all day thinking about "truth" and the nature of the universe. She imagines that marrying Casaubon will be like marrying "Pascal" (a great French philosopher), because he will teach her to "see the truth by the same light as great men have seen it by."